Flexible rolling of light metals

ABSTRACT

A method of flexibly rolling a metal strip or a metal sheet bar, wherein the metal strip or metal sheet bar is rolled in the longitudinal direction of the rolling operation along its entire length from a starting thickness to an end thickness which is variable along its length. The strip or sheet bar material used is in the form of light metals, more particularly aluminum or magnesium.

The invention relates to a method of flexibly rolling a metal strip or metal sheet bar wherein the metal strip or metal sheet bar is rolled in the longitudinal direction of the rolling operation along its entire length from a starting thickness to an end thickness which is variable along its length. This invention also relates to products produced in accordance with this method.

BACKGROUND OF THE INVENTION

A method of this type is known from German Publication DE 197 04 300 A1 wherein the starting material is first heated to a temperature in excess of the crystallization temperature and then rolled. After the hot rolling operation, the material structure is re-crystallized. In view of the fact that there is mentioned a re-crystallization temperature in excess of 700° C. it is clear that the starting material has to be assumed to be alloy steels.

From German Publication DE 299 13 509 U1 there is known a multi-roll stand which permits the so-called “flexible rolling” process in that the rolling gap is controlled during the rolling operation in accordance with a rolled strip thickness profile which changes along the length of the strip. The rolled strip can consist of steel or non-ferrous metals. German Publication DE 199 26 228 A1 proposes a method of rolling aluminum sheet or strip wherein the latter is provided with a non-uniform thickness profile transversely to the conveying direction and, additionally, in the longitudinal direction. For this purpose, it is necessary to use a stand with at least one working roll with different diameter regions transversely to the conveying direction of the aluminum sheet or strip.

OBJECT OF THE INVENTION

It is the object of the present invention to extend the field of application of the initially mentioned method and, more particularly, to especially adapt the method to selected light metal materials.

SUMMARY OF THE INVENTION

The objective is achieved by a method wherein the strip or sheet bar material used in the form of light metals and their alloys, more particularly aluminum or magnesium, and which is characterized in that the end thickness of the strip or sheet bar material comprises at least three different thickness stages. Between the individual thickness stages of constant thickness, there are provided regions of transition with variable thicknesses, more particularly with a gradient ranging between 1:40 and 1:4000 defined by thickness difference units over length units. The inventive products can be used, for example, for further improving the weight and strength optimization in motor vehicle construction. For instance, while the greatest thickness stage can be used for producing connections, several further thickness stages make it possible to achieve specific adaptations to different load application curves, which includes loads in the elastic deformation range and loads in crash cases involving plastic deformation.

It is important that, when carrying out this method, the thickness of the material be reduced by at least 5% along its entire length with reference to the starting thickness which is assumed to be 100%. In this way, there is achieved an intermediate product with an improved quality and an increased dimensional accuracy.

The differences in the end thickness of the material between thickness stages adjoining one another in respect of thickness should amount to at least 10%, preferably in excess of 20%, in order to produce specifically usable strength differences of the preliminary product for formed sheet metal parts to be produced therefrom.

Preferred thickness ranges for the at least three thickness ranges are mentioned below. The selection of concrete values primarily depends on the strength requirements for the end product to be produced from the inventive material.

The change in the different thickness stages can take place in any sequence on the sheet bar or strip material, with the sequence being periodically repeated in the strip material.

The maximum reduction in thickness of 70%, with reference to the starting thickness of 100%, should not be exceeded. In addition, a maximum gradient of the transition regions between the individual adjoining thickness stages of approximately 1:40 has to be observed. The proposed minimum gradient is 1:4000. In practice, values near the maximum gradient will prevail.

If the strip or sheet bar material is used in the form of aluminum, the material can be cold-rolled or, for hot-rolling purposes, it can be heated to a temperature ranging between 350° and 470° C.

If the strip or sheet bar material is used in the form of magnesium, the material can be cold-rolled or, for hot-rolling purposes, it can be heated to a temperature ranging between 180° to 280° C.

In the case of hot-rolling, the strip material can be preheated at the wound-up coil. However, it is also possible to heat uncoiled strip in a continuous process, more particularly in the case of induction heating.

Furthermore, the invention includes metal strip or metal sheet bar produced in accordance with this process as well as planar elements, tubes or profiles produced therefrom.

The flexibly rolled material can be cut to lengths or trimmed and processed further in different ways and is suitable for different uses. First, reference is made to German Publication DE 100 41 281 A1 according to which sheet bar of flexibly rolled metal strip can be formed by deep-drawing or other forming processes into profiles or dish-shaped elements. Furthermore, reference is made to the earlier German Publication DE 103 23 694 A1 according to which directly after the flexible rolling of continuous strip material the latter is formed into a continuous tube or profile and cut into individual tube or profile pieces. Furthermore, reference is made to German Publication DE 103 23 693 A1 according to which flexibly rolled material is formed into tube or profile members with out-of-round cross-sections. In addition, reference is made to German patent application 102004017343.5 dated Apr. 6, 2004 according to which, by deep drawing, flexibly rolled material is formed into a tube or profile whose cross-section is variable in the longitudinal direction. Finally, reference is made to German patent application 102004019448.3 dated Apr. 19, 2004 according to which hybrid metal plate elements of different parts are produced by using flexibly rolled material. Reference is hereby expressly made to the disclosure content of all the earlier patent applications by the same applicant. In the latter case, provided suitable joining technologies are used, it is also possible to produce hybrid elements which partly consist of flexibly rolled aluminum or magnesium and partly of steel plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the changes in strip or sheet bar material occurring during the rolling operation are illustrated in the drawings.

FIG. 1 illustrates a sheet bar or a strip portion prior to being rolled.

FIG. 2 illustrates a sheet bar or a strip portion after having been rolled.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a sheet bar or a strip portion 1 prior to being rolled, with its thickness in the form of the starting thickness being referred to as h0. From the starting thickness h0, the material, by flexible rolling, is rolled in one single rolling pass to three different thickness stages h1, h2, h3 with h0>h1>h2>h3, so that the following relationship exists: h1=h0−Δh₁, h2=h0−Δh₂ and h3=h0−Δh₃.

FIG. 2 shows a sheet bar or strip portion 2 after having been rolled, with a first portion 3 having a thickness h1=h0−Ah₁, a second strip portion 4 having a thickness h2=h0−Δh₂ and a third strip portion 5 having a thickness h3=h0−Δh₃. A first transition portion 6 with the length L₁ forms the transition from thickness h1 to thickness h2, with the idealized gradient having to be calculated to be _(γ1)=(h1−h2)/L₁.

A second transition portion 7 with the length L₂ forms the transition from thickness h2 to thickness h3, with the idealized gradient having to be calculated to be γ _(γ2)=(h2−h3)/L₂.

As the strip material is rolled along its entire length, the relationship h1<h0 exists. As can also be seen, the relationship h2<h1 and h3<h2 exists. The rolling direction can extend from portion 3 to portion 4 or vice versa. By means of a third transition portion (not illustrated), it is possible to change from thickness h3 to thickness h1. 

1. A method of flexibly rolling a metal strip or a metal sheet bar wherein the metal strip or metal sheet bar is rolled in the longitudinal direction of the rolling operation along its entire length from a starting thickness to an end thickness which is variable along its length, and wherein the strip or sheet bar material used is in the form of light metals, wherein said end thickness comprises at least three different thickness stages.
 2. A method according to claim 1, wherein the thickness of the material is reduced along its entire length by at least 5% with reference to the starting thickness of 100%.
 3. A method according to claims 1 or 2, wherein differences in end thickness of the material of different thickness stages are at least 10%, which thickness stages adjoining one another in respect of thickness, with reference to the starting thickness of 100%.
 4. A method according to claims 1 or 2, wherein the thickness of the greatest thickness stage ranges between 95% and 75% with reference to the starting thickness of 100%.
 5. A method according to claims 1 or 2, wherein the thickness of the second greatest thickness stage ranges between 85% and 45%, with reference to the starting thickness of 100%.
 6. A method according to claims 1 or 2, wherein the thickness of the second greatest thickness stage ranges between 85% and 45% with reference to the starting thickness of 100% and wherein the thickness of the third greatest thickness stage ranges between 75% and 30% with reference to the starting thickness of 100%.
 7. A method according to claim 6, wherein different thickness stages alternate periodically, but in any optional sequence.
 8. A method according to claim 6, wherein the changes in thickness between the individual thickness stages are carried out with a gradient γ of at most 1:40 and of at least 1:4000.
 9. A method according to claim 8, wherein the thickness of the material is reduced by a maximum of 70% with reference to the starting thickness of 100%.
 10. A method according to claim 6, wherein if aluminum is used, the material, prior to being rolled, is heated to a temperature of at least 350°-470° C.
 11. A method according to claim 6, wherein if magnesium is used, the material, prior to being rolled, is heated to a temperature of 180°-280° C.
 12. A method according to claim 6, wherein use is made of strip or sheet bar with a width in excess of 1400 mm transversely to the direction of rolling.
 13. A metal strip or metal sheet bar which, by being flexibly rolled in the longitudinal direction of the rolling operation, is rolled along its entire length from a starting thickness to an end thickness, which end thickness is variable along its length, wherein the strip or sheet bar material is used in the form of light metals, wherein the end thickness comprises at least three different thickness stages.
 14. A metal strip or metal sheet bar according to claim 13, wherein there exists differences in end thickness of the materials between thickness stages adjoining one another in respect of size of at least 10% with reference to the starting thickness of 100%.
 15. A metal strip or metal sheet bar according to any one of claims 13 or 14, wherein the thickness of the greatest thickness stage ranges between 95% and 75% with reference to the starting thickness of 100%.
 16. A metal strip or metal sheet bar according to claim 15, wherein the thickness of the second greatest thickness stage ranges between 85% and 45% with reference to the starting thickness of 100%.
 17. A metal strip or metal sheet bar according to claim 16, wherein the thickness of the third greatest thickness stage ranges between 75% and 30% with reference to the starting thickness of 100%.
 18. A metal strip or metal sheet bar according to claim 17, wherein the changes in thickness between the individual thickness stages take place with a gradient γ of at most 1:40 and of at least 1:4000.
 19. A metal strip portion or a metal sheet bar according to claim 18 which produces a deformed planar element consisting of sheet metal.
 20. A metal strip portion or a metal sheet bar according to claim 19 which produces a hollow profile or tube consisting of sheet metal. 